The invention relates to a metering pump assembly for admixing a fluid reduction agent into an exhaust gas flow
With self-ignition internal combustion engines, nitrogen oxides arise on operation with excess oxygen, which is the case in the majority of operating conditions, and specifically in particular with direct injection into the main combustion space, as is typically the case with diesel motors. In order to reduce these nitrogen oxide emissions, it is known to lead the exhaust gas flow to a reduction catalyser. Thereby, as a reduction agent, usually an aqueous urea solution is led in a finely distributed manner to the exhaust gas before entry into the catalyser. Thereby, the supplied quantity of urea is to be matched as precisely as possible to the combustion process, in order on the one hand to ensure an as complete as possible reduction within the catalyser, and on the other hand to prevent an excess of urea.
A special metering pump assembly for metering and feeding reduction agent to the exhaust gas flow is known from EP 1 435 458 A1. With this metering pump assembly, the supplied reduction agent, before feeding to the exhaust gas flow, is mixed or impinged with pressurized air in the metering pump assembly. In order to be able to firstly bleed the system on starting operation, a 3/2-way valve as a preflushing valve is arranged in front of a premixing device, in which the mixing of the reduction agent with pressurized air is effected. On starting operation of the assembly, this preflushing valve is firstly switched such that the metering pump conveys the aspirated reduction agent back into the reduction agent tank, until the conduits are completely filled with reduction agent. The premixing valve is then switched over, so that the reduction agent is supplied to the premixing device.
The object of the present invention is to simplify the construction of the metering pump assembly known from EP 1 435 458 A1.
This object is achieved by a metering pump assembly with the features specified in claim 1. Preferred embodiments are to be deduced from the dependent claims.